1. Field of the Invention
The present invention relates to an image capturing apparatus which has an electronic view finder function, a control method for the image capturing apparatus, and a computer program for the image capturing apparatus.
2. Description of the Related Art
Conventionally, an electronic still camera which has a moving image monitoring function, i.e. an electronic still camera which has a function (electronic view finder (EVF) or live view function) of outputting an image before image capturing to a monitor or the like, has been known.
In the electronic still camera, predetermined processing is performed on an image signal obtained by a complementary metal oxide semiconductor (CMOS) or a charge coupled device (CCD) by a data processing unit and the like, and then, the image signal is output to the monitor as a moving image. Exposure of the image output to the monitor is controlled by changing control parameters (accumulated time: Tv, aperture: Av, and International Standards Organization (ISO) sensitivity: Sv) so that the image signal becomes a predetermined value. A combination of the three control parameters is fixed in a program line, and, upon obtainment of a signal that causes the image signal to be the predetermined value, a value Ev of object luminance is determined from values of the control parameters, then a value Bv is also determined therefrom. Illustrated below is a relational expression between Ev and Bv and among Tv, Av, and Sv:Ev=Bv+Sv=Tv+Av. Therefore, Tv, Av, and Sv for capturing a still image set by the camera are different from Tv, Av, and Sv for a live view image.
Conventionally, it is possible to set a number of positions at which a rotor stably stops by a cogging torque when energization is cut off to ½ to a number of positions at which the rotor can stop when energization is maintained (Japanese Patent Application Laid-Open No. 01-164258).
However, when an aperture value is controlled based on settings set by a user, it is necessary to maintain the energization for a relatively long time during the live view. In this case, in a conventional electromagnetic driving aperture device which has a stepping motor of a one-two phase driving method, an operation becomes unstable when the energization is cut off at a stop position at which the rotor becomes unstable by discontinuation of the energization. In other words, there is a problem that an operation becomes unstable since it is difficult to specify whether shifting for one step caused by the cogging torque occurs in a small aperture direction or in an open direction.